The present invention relates to an apparatus for levitating an object by radiation pressure, such as sound waves, and to an apparatus for transporting a levitated object.
Japanese Unexamined Patent Publication No. 7-24415 discloses an apparatus for levitating an object. The apparatus includes a vibration device and a plate-like vibrator. The vibration device vibrates the vibrator to generate air pressure, which levitates an object. The surface of the levitated object that faces the vibrator is formed flat. The publication also discloses a transporting apparatus that moves levitated objects by blasting air or by producing traveling waves with the vibrator.
Japanese Unexamined Patent Publications No. 7-137824 and No. 9-202425 each disclose an apparatus for transporting a levitated object. Both apparatuses include parallel elongated plate-like vibrators. Each vibrator is vibrated by a transducer located in a corresponding vibration device. Each vibration device causes the corresponding transducer to generate traveling waves. Vibration of the vibrators generates air pressure and levitates a flat object. In this state, the object is transported. Also, a method for transporting a levitated object in which the above described levitating apparatus is mounted on a carriage is known in the art.
Japanese Unexamined Patent Publication No. 9-202425 discloses an apparatus in which transducers of all the vibration devices are connected to a common oscillator. The transducers are Langevin transducers that use piezoelectric elements. The transducers are vibrated at a resonance frequency, which vibrates vibrators at a required strength (amplitude).
A structure that has parallel vibrators needs several vibration devices and thus needs several transducers. To stably levitate an object, the vibrators must be synchronously vibrated at the same amplitude. Thus, in the apparatus of the publication No. 9-202425, the transducers of all the vibration devices are connected to the common oscillator. The oscillator sends excitation signals of the same amplitude and the same frequency to all the transducers.
However, due to errors produced when machining and assembling, it is difficult to manufacture identical vibration devices when the devices have transducers using piezoelectric elements. Therefore, the resonance frequency slightly differs from one vibration device to another. Therefore, although the transducers are connected to the common oscillator, an object cannot be stably levitated.
Japanese Unexamined Patent No. 5-146178 discloses an apparatus that includes a vibration motor. The motor has a first piezoelectric element and a second piezoelectric element, which are located on the stator. The first element excites a transducer, and the second element generates voltage in accordance with applied vibration. The second element is connected to an impedance element. The impedance of an electric circuit that includes the second piezoelectric element is changed by the impedance element. The resonance frequency of bending vibration is changed, accordingly.
In a vibration device that includes transducers having piezoelectric elements to excite vibrators, there are errors produced when machining and assembling parts. Therefore, horns that couple the transducers to the vibrators must be ground such that the resonance frequency of the device matches a desired value. Adjusting the frequencies takes long time when assembling the device and thus increases the cost. Also, the resonance frequency varies according to the load (an object to be transported) and the temperature. Therefore, even if the resonance frequency is adjusted to a desired value when assembling, the resonance frequency may be deviated from the desired value. If the apparatus has two or more parallel vibrators, the resonance frequency can be deviated from the first value by a relatively great amount.
Accordingly, it is an objective of the present invention to provide a transporting apparatus that stably levitates an object when the object is levitated by two or more vibration devices. Another objective of the present invention is to provide a transporting apparatus that stably transfers levitated objects.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an apparatus for levitating and transporting an object is provided. The apparatus levitates the object above the surfaces of a plurality of vibrators by air pressure of sound waves that are generated by the vibrators. The apparatus includes vibration devices and a common power source. Each of the vibration devices corresponds to one of the vibrators. Each vibration device includes a first transducer for vibrating the corresponding vibrator. Each transducer includes a super-magnetostrictive material. The common power source is connected to at least two of the first transducers for actuating the first transducers.
The present invention also provides another apparatus for levitating and transporting an object. The apparatus levitates an object above the surface of an elongated vibrator by air pressure of sound waves that are generated by the vibrator. The vibrator produces traveling waves. The apparatus includes a first transducer coupled to one end of the vibrator. The first transducer includes a piezoelectric element, which converts mechanical energy into electric energy. A transducer vibrates the vibrator. A second transducer coupled to the other end of the vibrator. The second transducer includes a changing element, which changes output voltage or output current for converting mechanical energy into electric energy. An external impedance element is connected to the piezoelectric element. The impedance of the external impedance element is variable. An oscillator is connected to the first transducer for vibrating the first transducer. A detector detects the vibration state of the second transducer. A controller controls at least one of the oscillator and the external impedance element based on the vibration state of the second transducer detected by the detector such that the output voltage or the output current of the changing element is greater than a predetermined value.